Mold for casting internal combustion engine crank shafts



Feb. 26, 1935. c. E. SORENSEN MOLD FOR CASTING INTERNAL COMBUSTIONENGINE CRANK SHAFTS 2 Sheets-Shet 1 Filed Feb. 5, 1934 INVENTOR. m 5 J WATTORNEY.

Feb. 26, 1935.

MOLD FOR CASTING INTERNAL COMBUSTION ENGINE CRANK SHAFTS c. E. SORENSEN1,992 677 Filed Feb. 5. 1934 2 sheets -sheet 2 Patented Feb. 26, 1935UNITED STATES MOLD FOR CASTING INTERNAL COLIBUS- TION ENGINE CRANKSHAFTS Charles E. Sorensen, Detroit, Mich., assignor to Ford MotorCompany, Dearbom, Mich., a corporation of Delaware Application February5,

7 Claims.

The'object of my invention is to provide a crank shaft especiallysuitable for use in multicylinder internal combustion engines,particularly V-type eight cylinder motors wherein a 90 degree four-throwcrank shaft is employed.

An important feature of my improved crank shaft is that it need bemachined only at its bearings, in contrast to the conventional shaftwhich is usually machined all over. This advantage results for thereason that the conventional shaft is formed as a forging whereas myimproved shaft is formed as a casting. The device or casting mold usedmaintains an accuracy not obtainable in forgings so that balancing aloneis required after the bearings have been machined.

A further feature of great importance in connection with this device isthat my improved crank shaft is cast with the axes of its three mainbearings not aligned with each other so that the casting when poured isdefinitely bowed. This bowed shape compensates for shrinkage uponcooling and allows the casting to assume a normal straight shape afterit has cooled.

A further object of this invention is to provide a novel moldarrangement, particularly the means for aligning the several parts ofthe mold, whereby an accuracy in casting may be maintained much higherthan heretofore available.

With these and other objects in view, my invention consists in thearrangement, construc-.

tion and combination of the various parts of my improved device, asdescribed in the specifications, claimed in my claims, and illustratedin the accompanying drawings, in which:

Figure 1 is a plan view of one of my improved mold assemblies, a portionthereof being broken away to better illustrate the construction of acrank shaft which is cast thereby.

Figure 2 shows a sectional view, taken on the line 2-2 of Figure 1,illustrating particularly the gate construction. whereby iron isconducted simultaneously to form the four crank shafts in the mold.

Figure 3 is a sectional view, taken on the line 3-3 of Figure 2.

Figure 4 is a fragmentary sectional view, taken on the line 4-4 ofFigure 3, and

Figure 5 is a sectional view, taken on the line 55 of Figure 2.

Referring to the accompanying drawings, I have used the referencenumeral 17 to indicate the three main bearings of an internal combustionengine crank shaft, especially suitable for use in a V-type eight clinder engine. The shaft 1934, Serial No. 709,765

is provided with four crank pins 18, each of these pins being spaced at90 degree intervals around the axis of the main bearings to provide whatis known as a four-throw 90 degree crank shaft. A plurality ofcounterweights 19 are provided, these counterweights being locatedopposite to each crank pin hearing. The counterweights are designed todynamically counterbalance the crank pins and associated heavy endsofthe connecting rods which are secured thereto.

Heretofore, somewhat similar shafts have been formed by the forgingprocess, however, the crank shaft shown herein is formed by the castingprocess. The casting of crank shafts of this character has beenattempted in the past but due to the irregular parting line invariablyrequired in casting a 90 degree crank shaft, no commercial applicationof this method was made. The method of casting herein disclosed differsfrom the conventional practice in that the mold is made entirely of aplurality of super-imposed plates, each formed of core sand, theseplates being accurately located one above the other in a predeterminedrelationship.

Two of such .core plates are required for each bearing of the shaftand'two of such plates are required for the risers. Consequently, atotal of sixteen core plates are required to form the mold for castingthe shaft shown. These plates have been given the reference numerals 1through 16, respectively, beginning with the lowermost plate. The numberof plates provided depends uponv the number of bearings on the shaft andwill, of course, vary with shafts of other design.

Referring to the drawings, particularly Figures 1 and 2, it will benoted that I have provided a metal bottom plate 20 upon which the coreplates comprising my mold rest. A metal top plate 21 is provided andfour tie rods 22 secure the metal plates 20 and 21 together therebyfirmly securing the core plates, 1 through 16, in position one above theother.

It will be noted that four crank shaft castings are formed in each moldassembly, the shafts being cast simultaneously from a single runner orsprue which extends down through the center of the group of core plates.

Each of the core plates 14 is formed of core sand in a suitable die ormold, which plate is then baked in the conventional manner. Referring toFigure 1, it will be noted that the bottom or numher one core plate isprovided with four depressions, formed one in each corner thereof, whichdepressions form the ends of the crank shaft castings. The number twocore plate has four aligned openings therein which form the front endbearing ofthe crank shaft. Plate number 3 is also provided with openingstherein which form the first crank pin and opposite counterweight. Ineach succeeding core plate suitable openings are provided to form onehalf of each balance weight and half of the adjacent bearing. It will benoted,

that from the fifth core plate on through the sixteenth, each plate isprovided with a central opening to form a spruce or runner 24 throughwhich iron is poured. The sixth and seventh core plates are providedwith four branch runners 23 whereby the iron is conducted to the fourcrank shaft molds. It will be noted that the point at which the iron isconducted to the molds is well above the bottom of each mold but stillslightly below the center of the crank shaft. It is very important thatthe iron be conducted in at this point as otherwise a porous casting atthe center bearing is believed unavoidable. An important feature of thisdevice is that the runners 23 are disposed several inches above thebottom of the sprue 24, whereby the iron is cushioned as it is pouredinto'the runner so as to prevent washing away of the sand of the cores.When the iron is poured into the rlmner, it forms a well four or fiveinches deep in plates 5 and 6 and consequently the iron which 'fiowsthrough the runners 23 does not sour away the sand in the bottom of thewell.

Each of the plates 15 and 16 is provided with openings for risers 25which form continuations of the crank shaft castings. The core plate 14is provided with a transverse passageway 26 therein which communicateswith a vertical opening 27 in the core plate 15, this vertical openinghaving a strainer block 28 fixed therein. The upper face of the strainerblock 28 is in communication with a relatively large chamber 29 which isformed in the plate 16. The top plate 21 is provided with suitableopenings therein which expose the chamber 29 together with each riser 25and the central runner 24.,

In pouring the casting, the molten metal is poured directly into thechamber 29 from which it flows through a plurality of openings 30 in thestrainer block 28 down through the opening 27 and into the passageway26. The metal then fiows to the aligned central openings in the coreplates and drops to the bottom of this passageway, or to core plate 4,filling the well up level with the branch runners 23 from which it fiowsradially therethrough into the molds proper. The iron fills up the fourmolds level with the passageways 23 and the pouring is continued untilthe iron level nears the top of all four of the risers 25 and the runner24. The unit is then allowed to slowly cool, it requiring between threeor four hours for the castings to solidify. .During this solidificationperiod the iron shrinks and liquid metal in the risers 25 supplies themetal to compensate for the shrinkage in the upper several bearings ofthe shaft. However, the majority of the metal which is supplied to takeup the shrinkage comes from the runner 24 which, as shown in Figure 3,resembles only a shell at the time the castings have become solid. It isvery important that the runner 24 is placed in the center between thefour castings, because if such runner is disposed next to one of thewalls of the mold then it would cool practically as rapid as thecastings. Inasmuch as practically all of the heat radiation required tosolidify the castings must radiate laterally through the core plates itmay readily be seen that the runner, being disposed at the center of thefour castings, will remain liquid much longer than the castingsthemselves. Thus, liquid metal is supplied to the castings while coolingto take up the unavoidable ature of solidification down to theatmospherictemperature. The core plates, being formed of dry sand, arequite rigid and quite incompressible. The crank pins are, of course,radially offset from the shaft center so that when the pins contract inlength, the shaft will become bowed unless the two opposite flanges orcounterbalance weights also close in toward each other, The rigidity ofthe dry sand core plates is sufficient to prevent such closing in at thecounterbalance portions but this rigidity is not sufiicient to preventthe crank cheek portions adjacent to the crank pins from contracting.Consequently-the shaft, if cast originally straight, would beconsiderably bowed when cooled down to room temperature. To overcomethis the shaft is cast with its axis bowed in a direction opposite toits normal dis torting movement so that when the shaft is cold the axisof the main bearings will be aligned with each other. This amounts toforming the mold so that the portions of the counterweights and flangeopposite each crank pin are slightly closer together than the length ofthe pin so that when the pin shrinks the crank cheeks will be paralleland the shaft main bearings aligned with each other.

Figures 1 and 3 that the Referring to Figure 1, it will be noted thatthe lowermost main bearing of the crank shaft has a cylindrical metalslug 31 cast therein, the purpose of which is to. solidify the metal inthis lower main bearing before the crank pin bearings directly abovehave time to solidify. This main bearing will therefore draw liquidmetal from the crank pin bearings as it shrinks upon cooling and therebyprevent a porous main bearing. The slug 31 is not inserted to form a.chill but rather to speed up the cooling of the lower bearing before theupper crank pin bearings solidify to thereby assure a supply of liquidmetal from the rurmer 24, through the crank pin bearings.

A very important feature in connection with my improved mold is themeans for aligning the core plates one above the other. It will be notedthat a pair of triangularly shaped keys 32 are formed in each evenlynumbered core plate with the exception of the top plate 16. These keysare placed into correspondingly shaped keyways 33 which are molded inthe odd numbered core plates. These keysand keyways are triangularlyshaped so as to accurately pilot the core plates one upon the other.Itwill be noted that core plates 2 and 3, 4 and 5, etc., are thussecured in alignment but that no keys extend between plates 1 and 2, 3and 4, etc; While such keys might be desirable it is not commerciallypractical to form a locater on both sides of each plate because informing one surface of the plate much be slicked off flush with the coremold face. Consequently, in order to pilot the slicked off faces of themolds upon each other, I have provided a pair of openings 34 in eachcore plate, these openings being located on a line transverse to theline adjoining the keys 32. Core sand tapered dowels 35 are adapted tobe inserted in these openings, as shown in Figure 5, to align thecoacting faces of plates '1 and 2, 3 and 4, 5 and 6, etc.

From Figures 1 and 2 it will be seen that a metal band 36 is clampedaround the numbers 4 and 5 core plates, this band having a pad 37 ateach corner thereof. The purpose of these pads is to reinforce thesecore plates at the comers. This reinforcing is desirable with these twoplates because in the particular arrangement shown the heavy section ofthe lower counterbalancing weight 19 is so orientated that the thinadjacent section of the core might be washed out bythe flow of metaltherein; Of course, the core plates could be made larger to overcomethis; however, it is commercially desirable to keep the core plates assmall as possible and inasmuch as the counterweights weaken only two ofthe core plates the reinforcing band is desirable as it reduces theoverall size of all sixteen of the plates an appreciable amount.

Among the many advantages arising from the use of my improved device, itmay be well to mention that with the arrangement shown herein I am ableto commercially cast a four-throw crank shaft from alloy steel, whichshaft is believed to be commercially impossible to cast by theconventional foundry practice. Further, by locating the main running inthe center of a group of castings, the runner is prevented fromsolidifying until after the castings solidify to thereby allow the metalin the runner to compensate for shrinkage in the castings. A furtherimportant feature of the device is that the well at the bottoni of therurmer cushions the iron therein and thereby prevents the molten ironfrom scouring off sand of the cores and conductment, construction andcombination of the va-,

rious parts of my improved device without departing from the spirit ofmy invention and it is my intention to cover by my claims such changesas may reasonably be included within the scope thereof.

I claim as my invention:

1. A device for casting engine crank shafts having a plurality ofaxially aligned main bearing sections spaced therealong with an axiallyofiset crank section connecting said main bearing sections, comprising,a mold formed from baked core sand having a metal receiving cavitytherein which is similar in shape to the shape to be formed but whichdiffers therefrom in that the portions of said cavity which cast themain bearing sections of the shaft are sufficiently out of axialalignment that lengthwise contraction of the crank pin section, due tocooling, stresses said crank pin and causes the shaft to warp to aposition where the main bearing sections are in axial alignment.

2. A device, as claimed in claim 1, wherein mold is formed from aplurality of superimposed core sand discs, said discs having depressionstherein which form the crank arms of the shaft and having openingstherethrough which form the main and crank pin bearings of the shaftbeing cast. I

4. A mold for casting engine crank shafts having a plurality of axiallyaligned main bearing sections spaced therealong and having axiallyofiset crank pin .bearing sections and counterweights integraltherewith, comprising, a plurality of superimposed baked core sand discseach of which is provided with communicating depressions therein andopenings therethrough, the walls of said depressions and openingsforming a casting chamber of a shape similar to the shaft to be cast butdiffering therefrom in that the axes of the main bearing portions of thechamber are out of axial alignment sufficiently that the lengthwisecontraction of said crank pin portions due to the cooling of the shaftwill warp the castingsumciently to cause axially alignment of the mainbearing portions when the shaft is cold.

5. A self aligning mold for casting internal combustion engine crankshafts comprising, a plurality of baked core sand discs disposed oneabove the other, each of said discs whenproperly aligned havingcommunicating depressions therein and openings therethroughwhichformaplurality of casting chambers, each of said chambers beingsimilar in shape to the shaft being cast, and each of said discs beingcharacterized in that one of its faces is raked flat with saiddepressions formed entirely in the opposite face, and said discs beinglocated one above the other with their raked faces adjacent and with thedepression containing faces adjacent, the joint formed between each pairof depressions containing faces being angularly po-- sitioned by meansof integral keys and keyways formed on said faces while the joint formedbetween each pair of raked faces is angularly positioned by means ofdetachable core sand dowels.

6. A self aligning mold comprising, a plurality of baked core sand discsdisposed one above the other, said discs when properly aligned havingcommunicating depressions therein and openings therethrough which formthe casting chamber, and each of said discs being characterized in thatone of its faces is raked flat with said depressions being formedentirely in its opposite face, and said discs being located one abovethe other with their raked faces adjacent and with their depressioncontaining faces adjacent, the joint formed between each pair ofdepression containing faces being angularly positioned by means ofintegral keys and keyways formed in said adjacent faces respectively,and detachable means for angularly positioning each of said raked faceswith respect to its adjacent raked face.

7. A mold, as claimed in claim 6, wherein the means for positioning saidraked faces comprises a plurality of baked sand dowels.

CHAS. E. SORENSEN.

